Documentation: drm: Remove dangling pointer from drm-mm.rst

Fixes htmldocs build error:
Error: Cannot open file ../drivers/gpu/drm/drm_global.c

Fixes: 2bb4241 ("drm: Remove drm_global.{c,h} v2")
Cc: Thomas Zimmermann <[email protected]>
Cc: Christian König <[email protected]>
Cc: Junwei Zhang <[email protected]>
Cc: Alex Deucher <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Maxime Ripard <[email protected]>
Cc: Sean Paul <[email protected]>
Cc: David Airlie <[email protected]>
Cc: Christian Koenig <[email protected]>
Cc: Huang Rui <[email protected]>
Cc: [email protected]
Signed-off-by: Sean Paul <[email protected]>
Reviewed-by: Christian König <[email protected]>
Signed-off-by: Dave Airlie <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Documentation/gpu/drm-mm.rst

@@ -79,9 +79,6 @@ count for the TTM, which will call your initialization function.
 
 See the radeon_ttm.c file for an example of usage.
 
-.. kernel-doc:: drivers/gpu/drm/drm_global.c
-   :export:
-
 
 The Graphics Execution Manager (GEM)
 ====================================